This invention relates generally to the transfer of toned electrostatic latent images from the electrophotographic member on which it is formed to a secondary carrier. This invention particularly is concerned with the provision of the secondary carrier formed as a transparent sheet of stabilized polyester sheet material having a heat softenable compatible resinous coating applied to a surface thereof, the secondary carrier capable of receiving substantially complete transfer of a toned image from the electrophotographic member without loss of optical density or resolution, the toned image being embedded in the coating.
Various processes have been proposed for producing an image upon a substrate, including photographic processes involving actinic exposure of a photosensitive material carried on a substrate or electrostatic process involving exposing a charged electrophotographic member having a photoconductive surface coating or layer to radiation to produce an electrostatic latent image. This latent image is rendered visible by application of dry toner particles thereto as in cascade type development, or by wet application thereto of a liquid toner suspension wherein the toner particles have electrophoretic properties.
The production of suitable transparencies heretofore commonly requires the skill of a trained technician and the substantial expenditure of money and time. Photographic reproduction processes require controlled exposure, development, washing and fixing of a light sensitive composition present on a support with or without the intermediate production of a negative image.
Xerographic processes have proven to be an easy and reliable technique for the production of reproductions. Notwithstanding the desirability of these imaging processes, drawbacks have been encountered in forming transparencies in that the adherence of the image on the transfer support leaves much to be desired. Additionally, some loss of optical density and resolution is experienced upon transfer of the toned image to a receiving member employing prior methods.
Electrophotographic processes require the provisision of a suitable image carrier upon which images are formed, these carriers being required to accept an electrical charge and retain the charge sufficiently to enable image to be formed by application of toner particles thereto. Many materials displaying photoconductivity will not accept a charge initially, and of those which may be charged, few are capable of retaining the charge thereon without leaking off or decaying so rapidly as to be almost useless. In addition to accepting a charge and retaining the charge in darkness, the photoconductive layer is required to discharge in light areas to a degree which is fairly rapid and generally proportional to the amount of light to which the surface is exposed impinging upon the charged surface. Further, there must be retained a discernible difference between the remaining charged and uncharged layers without lateral movement of the charges.
With the advent of the electrophotographic member disclosed and claimed in U.S. Pat. No. 4,025,339, same being incorporated herein by reference herein to provide details of the said electrophotographic member, and particularly the electrical anistropy of the patented coating effectively resulting from the field domain of each crystal of the coating which functions independently in the charge and discharge mode without communicating laterally with contiguous crystals. The toner particles thus are attracted by myriads of individual fields in a magnitude dependent upon the magnitude of the individual field strengths of these individual fields enabling the obtaining of resolution heretofore unobtainable by electrophotographic reproduction.
Imaging, toning and transfer of the toned image to a carrier medium using the electrophotographic member of U.S. Pat. No. 25,339 documented in several of the additional patents listed earlier, each of which are incorporated herein by reference to show the method of employing said recording member for forming reproductions of original images.